Free shipping in the United States

Pool Water Chemistry Basics

Pool Water Chemistry
By Pools Above Ground
More from this author

Pool Water Chemistry Basics

The Basics of Pool Chemistry

Whether you have an above ground pool or inground pool proper precautions should be taken any time you are dealing with chemicals, particularly if you or your loved ones will be exposed to them. Indeed, mastering the chemistry associated with pool maintenance is one of the hardest parts of owning a pool. In fact, in some cases, we might make perfectly innocent mistakes that can end up having disastrous consequences. If you're new to swimming pool ownership or just want to get a better handle on "pool chemistry," we've created this handy guide to help you out. Not only will we cover some very helpful "dos" in the next few paragraphs, but we'll warn you of some very important "don'ts" as well.

The Importance of Pool Chemistry

No matter your past experience with swimming pools, you should have some understanding of the importance of using the right chemicals (in the right proportions). After all, doing so ensures that your swimming pool water is healthy enough for humans and unhealthy enough to resist the growth of bacteria, fungi, and algae. Indeed, there are many scenarios in which the wrong water balance can cause serious problems. That’s why it’s important to test your pool water frequently using specialized pool testing strips. The good news for above ground pool or vinyl liner pool owners is that water chemistry is typically simplified when dealing with vinyl liners as opposed to concrete walls and floor. With above ground pools there's nothing leaching out of the vinyl like there is with concrete. Going forward, we’ll take a look at some specific chemical scenarios and tell you what you should do if you encounter them during testing. Each situation will predominantly focus on four factors:


The pH level of your pool water refers to its acidity. It is measured on a scale from 0 to 14, with anything below 7.0 denoting acidity and anything above 8.0 being basic. Generally, you want your pool’s pH to be between 7.4 and 7.6.


his refers to your pool’s ability to withstand changes in pH. As alkaline substances act as buffers to these changes, you want your pool to register between 80 and 120 ppm (parts per million).

Calcium Hardness

The "hardness" of your pool's water refers to how much calcium is present. The ideal range is between 200 and 400 ppm.


Chlorine is the most common chemical for treating swimming pool water. As a disinfectant, it eliminates algae and bacteria while oxidizing dirt and other foreign particles.

Elevated pH and Low Chlorine

This chemical combo creates the ideal environment for algae blooms. These not only cloud your pool water, but they can turn it into a green, slimy mess. To deal with this issue, you’ll want to reduce the pH by adding an acid component. The strength of the acid will depend on the alkalinity of your water. If it’s too high, only the most powerful (and dangerous) of acids will do the trick.

Elevated pH and Elevated Calcium

In situations where your pH and calcium are reading high, your pool may develop a thin film on the surface and pipes. If you don't deal with this film right away, it can form crystallized calcium nodules that will need extensive work to remove. To solve this problem, you'll want to add a sequestering agent to minimize the effect of the elevated calcium levels. While it won't actually remove the calcium, it will make it far less likely that the substance will crystalize.

Low pH and Low Alkalinity

This is the perfect recipe for corrosion. This chemical combo will not only destroy everything from rubber to steel, but it can also cause your water to become highly acidic. In fact, if your pool every reads a pH of under 7, it's a good idea not to allow anyone to use it until the situation is resolved. To solve this issue, you'll need to add an alkalinity proponent such as sodium bicarbonate. However, this particular chemical will only work on concrete pools. For vinyl or fiberglass models, a dry acid should be introduced until the alkalinity returns back to the 80-120 range.

Low pH and High Alkalinity

Though similar to the situation outlined above, the high alkalinity present in this scenario will make it more difficult to raise your pH levels. Remember, alkalinity acts as a buffer to prevent the water’s pH from changing! For this reason, the only way to lower your water's alkalinity is to remove carbonates present in the pool. A good way to do this is to aerate the water. You can rent specific aerating tools at affordable rates or purchase them in the event the problem reoccurs.

Elevated Combined Chlorine

This refers to a situation in which chlorine is present in the pool but cannot sanitize the water. In a way, the chemical remains, but its bacteria and algae-fighting abilities are diminished or eliminated. If chlorine levels reach 3 ppm or above, the only real solution is to "shock" your pool. This is the term for raising the level of chlorine far beyond previous levels to remove all contaminants in one fell swoop. You will, of course, have to keep swimmers out until the chlorine levels subside again.

Low Calcium Hardness

Again, this will create a highly-corrosive environment that can destroy pool equipment and eat away at vinyl liners. To solve this problem, you’ll need to purchase a calcium hardness product and follow the instructions to the letter. Regarding Chlorine Shock If you're performing a chlorine shock, it's important that you avoid adding an algaecide to the process. This will not only be a waste of money (as the chlorine will devour the algaecide in seconds) but could cause an unanticipated reaction. For the same reasons, it’s also important that you avoid combining the shock process with a sequestering agent of any kind. Instead, wait until a few days after shocking your pool to add these in.

In Conclusion

Every pool is a petri dish – an environment all its own. In order to deal with problems that you might encounter throughout the ownership of your swimming pool, you should ensure you have a basic knowledge of chemistry at work inside. In the end, nothing can make up for regular testing of your pool's water when it comes to getting ahead of any chemical issues. If you have any questions about your above ground or semi-inground pool please contact us at or expert advise.
December 30, 2020